Transparent, oriented films made from crystallizable thermoplastics of thickness from 1 to 300 μm are well known.
These films comprise neither UV stabilizer as light stabilizer nor flame retardants. For this reason, neither the films nor the items produced from them are suitable for outdoor applications where fire protection or low flammability is a requirement. The films do not pass the fire tests of DIN 4102, Part 2 and Part 1, nor that of UL 94.
In outdoor applications, even after a short period, the known films show yellowing and a deterioration in mechanical properties, due to photooxidative degradation by sunlight.
EP-A-0 620 245 describes films with improved heat resistance. These films comprise antioxidants suitable for scavenging free radicals formed in the film and for degrading any peroxide formed. However, this specification makes no proposal as to how the UV resistance of films of this type may be improved.
DE-A 23 46 787 describes a low-flammability plastic. Besides the plastic, the claims also cover the use of the plastic to give films and fibers.
However, when films were produced from this phospholane-modified polymer as claimed in said publication the following shortcomings were apparent:
The plastic is very susceptible to hydrolysis and has to be very thoroughly predried. When the plastic is dried using dryers of the prior art it cakes, and if production of a film is possible at all it is possible only under very difficult conditions. The films produced under extreme, and uneconomic, conditions embrittle at high temperatures, that is to say their mechanical properties decline sharply as a result of rapid embrittlement, making the film unusable industrially. This embrittlement arises after as little as 48 hours at high temperature.